1. Field of the Invention
The present invention relates to a parallel hybrid drive for a motor vehicle including a drive train with an internal combustion engine and an electric machine connected to a transmission, wherein a first clutch is arranged in the drive train between the internal combustion engine and the transmission and wherein the transmission is arranged between the first clutch and the electrical machine.
2. Description of the Related Art
A prior art parallel hybrid drive is disclosed in DE 195 30 233 A1 and has a drive unit including an internal combustion engine, a transmission, an electrohydraulic disengaging clutch which is used as a "first clutch" connected between the internal combustion engine and the transmission and an electric motor. The electric motor of the drive unit acts directly on the drive shaft of the transmission via a gear wheel layshaft stage without the interposition of a clutch. The internal combustion engine also acts on the drive shaft of the transmission via the disengaging clutch. The electric motor is connected to a power supply unit having batteries and a current regulating unit and may be used as a drive motor, a generator for charging the batteries when the internal combustion engine is being operated, a starter motor for the internal combustion engine, and a synchronizing device for the transmission.
Another prior art parallel hybrid drive for a motor vehicle is disclosed in DE 195 03 501 A1. A drive train in this prior art parallel hybrid drive includes an internal combustion engine, a clutch designed as a freewheeling device and whose rotation direction can be changed, an electrical machine of the external rotor type, a disengaging clutch and a transmission following one another. The motor vehicle may optionally be driven by either the electrical machine--which then acts as an electric motor--or by the internal combustion engine on its own. When the motor vehicle is driven by the electrical machine, the internal combustion engine is stopped and the freewheeling clutch is disengaged. When the motor vehicle is being driven by the internal combustion engine, the freewheeling clutch is closed and the electrical machine is either not energized or operated as a generator. The freewheeling clutch may have an associated bridging clutch such that the electrical machine may optionally drive the internal combustion engine while the electrical machine is driving the motor vehicle when the bridging clutch is closed. The bridging clutch allows the internal combustion engine to be started by of the electrical machine. A claw clutch which can be engaged and disengaged by an electromagnet, for example, is mentioned as the bridging clutch.
The electrical machine of this known parallel hybrid drive comprises a stator with field windings which is held by the housing of the internal combustion engine and encloses the freewheeling clutch. A permanent-magnet external rotor of the electrical machine is fitted with a clutch housing for the disengaging clutch. The freewheeling clutch or the bridging clutch directly connects a shaft of the rotor to the crankshaft of the internal combustion engine. On the transmission side, the rotor acts directly via the disengaging clutch on the input shaft of the transmission. With the exception of the rotor shaft, which may also be regarded as an extension of the crankshaft, neither an electric motor shaft on the internal combustion engine side nor an electric motor shaft on the transmission side may be associated with the electric motor. Seen overall, the electrical machine of this prior art hybrid drive is not a structurally and functionally autonomous unit with respect to the internal combustion engine, the disengaging clutch and the transmission.
With regard to further prior art parallel hybrid drives having an electric motor arranged between the internal combustion engine and the transmission, reference is made to DE 29 43 519 A1 and DE 43 23 602 A1. In DE 29 43 519 A1, the electric motor has an associated freewheeling mechanism which separates the synchronization of the transmission from the moment of inertia of the electric motor. In DE 43 23 602 A1, the electrical machine is integrated in a friction-clutch arrangement which connects the crankshaft of an internal combustion engine to the transmission input shaft of a transmission.
In general, if the electrical machine of a hybrid drive is required to rotate during internal combustion engine operation, losses occur either from the fact that unavoidable iron losses occur in the unenergized electrical machine or from the fact that the fuel energy is not optimally converted into electrical energy because the efficiency of the electrical machine when operating as a generator is not optimum.